1. Field of the Invention
The invention relates to a method for manufacturing a film, and more particularly, to a method for manufacturing an electret diaphragm for an electret electro-acoustic transducer.
2. Description of the Related Art
Loudspeakers are a kind of device to make sound. The principle of making sound for the loudspeakers is to vibrate the diaphragms thereof by electrical signals to push the air. Nowadays, the loudspeakers have been broadly used in the electronic devices with the function of making sound, such as mobile phones, personal digital assistants (PDAs) and laptop computers.
One of the common loudspeakers is so-called dynamic loudspeaker. The principle of making sound for the dynamic loudspeaker is to drive a current through the voice coil to produce a magnet field. This magnetic field causes the voice coil to react to the magnetic field from a permanent magnet fixed to the frame of the loudspeaker thereby vibrating the diaphragm attached with the voice coil so as to make sound. Although such dynamic loudspeaker can provide very good quality of sound, the loudspeaker has a considerable thickness because its sound chamber is large. When such dynamic loudspeakers are used in the above portable electronic devices, the thickness of these electronic devices cannot be reduced.
In order to solve the above problem, a so-called electret loudspeaker is manufactured. The electret loudspeaker includes a flexibly dielectric film to act as a diaphragm. The dielectric film has a conductive material formed thereon to function as an electrode. After the conductive material is formed, the dielectric film is polarized to generate static charges therein and thereon. A discussion about the electret loudspeakers can be found on the Taiwan Patent No. I293233, entitled “FLEXIBLE LOUDSPEAKER AND ITS FABRICATING METHODS”.
However, the diaphragm manufactured by the conventional processes has a problem that the conductive material is prone to come off the dielectric film. This will lead to an adverse effect on the performance of the electret loudspeaker. Furthermore, the mass production of the electret loudspeakers is hard to be achieved by conventional processes.